How to hide "gaps" between parts of my detail?
It sems you have have overlapping vertices, which creates a seam in the topology when rendering.

Notice the black line between the edges which cause problem in edit mode are darker than the other ones.
Select all your vertices with  A  in edit mode and vertex select mode, and Press  ALT  +  M  (or right click > Merge vertices) then choose "by distance" in order to eliminate double-vertices.